The present invention is directed to apparatus for achieving staggered firing of spark plugs in a dual-plug spark internal combustion ignition engine, and more particularly to a low-cost control implementation that requires only a single output from the engine control module.
In general, a dual-plug engine is a spark-ignition internal combustion engine that is equipped with two spark plugs per cylinder in order to achieve improved performance and/or exhaust emission control. Although these improvements can be optimized when the two spark plugs are fired in staggered relation, the expense associated with individual spark plug control can be considerable because the number of coil driver circuits (ignitors) and engine control module (ECM) outputs is doubled. The cost impact is particularly high in applications where the ignitors are up-integrated into the ECM due to packaging difficulties and increased heat dissipation in the ECM. Accordingly, what is needed is a more cost effective control apparatus that achieves staggered spark plug firing without increasing the number of ECM outputs, and without requiring additional up-integrated ignitors in the ECM.
The present invention is directed to an improved control apparatus for achieving staggered spark plug firing in a dual-plug spark ignition engine wherein first and second spark plugs for any given engine cylinder are controlled by a single ECM output. The ECM output initiates firing of the first spark plug, and a detection and delay circuit packaged with an ignition coil and ignitor for second spark plug initiates delayed firing of the second spark plug relative to the first spark plug. In a preferred embodiment, the detection and delay circuit also detects engine speed based on the firing frequency of the first spark plug, and adjusts the firing delay time so that the firing of the second spark plug is delayed with respect to the firing of the first spark plug by a calibrated angle of engine rotation.